The Rewrite Rule Machine (RRM) is a massively parallel MIMD/SIMD computer designed with the explicit purpose of supporting very high-level parallel programming with rewrite rules. The RRM's node architecture consists of a SIMD processor, a SIMD controller, local memory, and network and I/O interfaces. A 64-node cluster board is already an attractive RRM system capable of extremely high performance on a variety of applications. A cluster is SIMD at the node level, but it is MIMD at the system level to flexibly exploit the parallelism of complex nonhomogeneous applications. In addition to reporting detailed simulation experiments used to validate the node design, we measure the performance of an RRM cluster on three relevant applications.